P89LPC9331_9341_9351_9361 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2012. All rights reserved.
Product data sheet Rev. 5.1 — 20 August 2012 46 of 94
NXP Semiconductors
P89LPC9331/9341/9351/9361
8-bit microcontroller with accelerated two-clock 80C51 core
7.23.7 Break detect
Break detect is reported in the status register (SSTAT). A break is detected when
11 consecutive bits are sensed LOW. The break detect can be used to reset the device
and force the device into ISP mode.
7.23.8 Double buffering
The UART has a transmit double buffer that allows buffering of the next character to be
written to SnBUF while the first character is being transmitted. Double buffering allows
transmission of a string of characters with only one stop bit between any two characters,
as long as the next character is written between the start bit and the stop bit of the
previous character.
Double buffering can be disabled. If disabled (DBMOD, i.e., SSTAT.7 = 0), the UART is
compatible with the conventional 80C51 UART. If enabled, the UART allows writing to
SBUF while the previous data is being shifted out. Double buffering is only allowed in
Modes 1, 2 and 3. When operated in Mode 0, double buffering must be disabled
(DBMOD = 0).
7.23.9 Transmit interrupts with double buffering enabled (modes 1, 2 and 3)
Unlike the conventional UART, in double buffering mode, the TI interrupt is generated
when the double buffer is ready to receive new data.
7.23.10 The 9
th
bit (bit 8) in double buffering (modes 1, 2 and 3)
If double buffering is disabled TB8 can be written before or after SBUF is written, as long
as TB8 is updated some time before that bit is shifted out. TB8 must not be changed until
the bit is shifted out, as indicated by the TI interrupt.
If double buffering is enabled, TB must be updated before SBUF is written, as TB8 will be
double-buffered together with SBUF data.
7.24 I
2
C-bus serial interface
The I
2
C-bus uses two wires (SDA and SCL) to transfer information between devices
connected to the bus, and it has the following features:
• Bidirectional data transfer between masters and slaves
• Multi master bus (no central master)
• Arbitration between simultaneously transmitting masters without corruption of serial
data on the bus
• Serial clock synchronization allows devices with different bit rates to communicate via
one serial bus
• Serial clock synchronization can be used as a handshake mechanism to suspend and
resume serial transfer
• The I
2
C-bus may be used for test and diagnostic purposes.
A typical I
2
C-bus configuration is shown in Figure 14. The P89LPC9331/9341/9351/9361
device provides a byte-oriented I
2
C-bus interface that supports data transfers up to
400 kHz.
